In the field of manufacturing carpet, it is well known that the yarns used are heated and stretched to attain as high a tensile strength as possible, thereby yielding a stronger filament. In so heating and stretching the yarns, the yarn is taken from a supply spool, wrapped around a pre-heating spool, and then wrapped around a final heating spool. It is well known that currently, the final heating spool is capable of achieving surface temperatures in the range of 200.degree. C. to 230.degree. C. The heating elements used to heat the final heating spools are capable of attaining temperatures in the range of 300.degree. C. to 500.degree. C.
It is well known that the heating capacity of the yarns is somewhat higher than that currently attainable by existing heaters. Therefore, it is desirable to provide a heater which may be used to heat the surface of the final heating spool to at least the maximum temperature allowable for the selected material being heated.
Devices currently used include transformers composed of insulated copper wires wrapped a selected number of times to induct heat into the associated spool. The physical characteristics of these transformers limit their heating capacities. The insulation used on these transformers has a temperature limit at which cracks form. With cracks and other defects in the insulation, the copper wire is allowed to oxidize, thereby creating breaks in the wire, which yield the transformer useless. The deficiencies of the insulation are costly, as they may require much shut-down time for the associated machinery, and may be otherwise expensive to correct.
The wire used in typical devices has also posed a problem. Copper wire is known to be an excellent conductor of heat. However, when exposed to air, it is also well-known to be prone to oxidation. Again, the protection of the copper wire from such adversities is a function of the insulation, and the insulation typically used is inadequate.
Other devices have been produced to overcome these problems, such as those described in U.S. Pat. No. 3,412,228 issued to H. Miyagi on Nov. 19, 1968, and U.S. Pat. No. 3,412,229 issued to E. M. Seagrave, Jr., on Nov. 19, 1968. Still, these devices are not capable of reaching the desired level of output temperatures.
Other similar heaters are known in the art such as those described in U.S. Pat. No. 4,788,394 issued to G. Vanneste, et al., on Nov. 29, 1988, and U.S. Pat. No. 4,948,466 issued to J. Jaakkola on Aug. 14, 1990. Though each of these discloses an induction heater incorporating ceramic materials, neither is sufficient for the purposes of the present invention. The '394 patent discloses a multiwire induction heater designed to heat steel wires of a diameter between 0.5 and 3 mm to temperatures not exceeding 750.degree.-760.degree. C. The '466 patent discloses a heater for use in the paper manufacturing field and is designed to attain temperatures in the range of 140.degree.-500.degree. C. In the field of the present invention, it is desirable to attain temperatures up to 1000.degree. C.
Polyester cords used in the manufacture of tires are processed similarly to the yarns used in the manufacture of carpets. The equipment used for processing these cords are limited in like fashion to those described above. Other filaments may also require similar processing.
Therefore, it is an object of this invention to provide a means for heating a selected filament to its maximum associated temperature in order to insure a maximum tensile strength from the selected filament.
Another object of the present invention is to provide such a means for heating a selected filament wherein a transformer is used as a heating source.
Still another object of the present invention is to provide such a transformer wherein copper wire may be used, the copper wire being protected from oxidation.
Yet another object of the present invention is to provide a means whereby the individual turns of the copper wire are insulated one from the other, the insulation being capable of withstanding the desired output temperatures of the transformer.